Stress Sensor Bridge Circuit for Simplified Wafer Monitoring
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Solution Overview
Problem
Conventional stress sensors for semiconductor wafers require complex precision current supplies and readout circuits, leading to increased complexity and potential measurement errors due to sensitivity to mechanical stresses, making them difficult to operate and array for large-scale stress monitoring.
Innovation Solution
A stress sensor circuit with a bridge circuit configuration, including orthogonal resistors and a tunable switched capacitor resistor, which generates a voltage output based on mechanical stress, allowing for simpler operation and higher sensitivity without the need for precision current supplies, and enabling easier arraying for large-scale measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional stress sensors with precision current supplies and readout circuits are used, then measurement precision can be maintained, but device complexity increases significantly
Solution Approach 1:
The patent extracts the stress sensing function from complex precision current supply and readout circuits, implementing it directly in the sensor structure itself through differential voltage measurement. This removes the need for external precision current sources while maintaining measurement accuracy.
Solution Approach 2:
The sensor structure serves multiple functions: it acts as both the stress sensing element and the measurement circuit. The differential voltage output inherently provides both the measurement signal and the reference, eliminating the need for separate precision reference circuits.
2Area of stationary object
If multiple stress sensors are implemented in arrays, then coverage of large structures improves, but routing complexity of precision current supplies and readout signals increases
Solution Approach 1:
The patent segments the monitoring function into independent sensor units, each capable of autonomous differential voltage measurement. This modular approach allows sensors to be distributed across large areas without requiring complex shared current supply routing, as each sensor is self-contained.
3Device complexity
If on-chip current sources are used to simplify routing, then device complexity reduces, but measurement precision deteriorates due to sensitivity to mechanical stresses
Solution Approach 1:
The patent replaces the mechanical/current-based sensing approach with a voltage-based differential measurement system. Instead of using current sources that are sensitive to mechanical stress, the sensor directly measures differential voltages that are inherently more resistant to mechanical interference.
4Device complexity
If shared current- and voltage-monitoring wiring is used, then device complexity reduces, but measurement precision is compromised due to requiring multiple measurements and physical switching
Solution Approach 1:
The patent employs periodic modulation of the excitation signal, allowing the sensor to multiplex multiple measurements through time-division rather than requiring complex physical switching. This maintains measurement precision while simplifying the wiring architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides enhanced sensitivity and simplicity in stress monitoring, reducing measurement errors and complexity, while maintaining stability against temperature and radiation variations, and allowing for micro-scale monitoring of local stresses in larger mechanical structures.
Implementation Method 1
The resistors comprise piezo-resistive strips arranged in particular crystallographic directions
Data Source
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Figure 2A
Figure 2B
AI summary
A stress sensor (100) is provided, including a substrate (102) and a bridge circuit (110) disposed thereon. The bridge circuit is coupled between an output node (Vout) and a ground node (GND). The bridge circuit (110) includes a first branch (112) and a second branch (114), the first having a first resistor, R1, having a first orientation and coupled to a tuning resistor, Rtune, at a first intermediate node (120). The second branch (114) includes a second resistor, R2, having a second orientation that is different from the first orientation, and coupled to a variable resistor, Rvar, at a second intermediate node (130). The bridge circuit (110) includes an amplifier (140) having a positive input terminal coupled to the second intermediate node (130), and a negative input terminal coupled to the first intermediate node (120). The amplifier (140) generates a voltage output at the output node (Vout) as a function of mechanical stress applied to the substrate (102). Rvar is non-linearly tunable based on the voltage output.